The present invention relates to a method for manufacturing a light alloy automotive wheel having an annular hollow portion provided in an outer rim portion thereof, and a wheel manufactured by the method.
As light alloy automotive wheels which are made of materials such as aluminum and magnesium are light in weight and good in machinability, wheels having superior designs have been provided, and the mounting ratio of such light alloy automotive wheels is so increased that they are mounted on production lines. However, external shapes of outer rims, such as shapes of a bead seat, a hump, a slope from the hump to a rim well and an inner surface of a rim flange, on which a tire is mounted, are regulated by the international standard made by European Tire and Rim Technical Organization (ETRTO), and in order to secure a regulated rigidity at these portions of a rim, the rim is constructed to have a certain thickness. Although the thickness of the rim only has to be increased in order to increase the rigidity of the rim, increasing the thickness results in an increase in weight of the rim and an increase in unsprung weight, leading to a risk that the steering performance is lost remarkably. To solve the problem, there have been proposed a technique in which a hollow portion is provided in a rim portion to suppress the increase in weight while increasing the rigidity. As the related arts, there are raised JP-A-5-278401 and JP-2003-527269T (Japanese translation Publication of WO01/017799). The crux of these techniques is to establish a communication between hollow portions in a spoke portion and a rim portion. In the former technique, due to a limitation imposed by a casting method, an outer rim portion and an inner rim portion are cast separately, and thereafter, they are integrated with each other by a friction welding method to complete a wheel. In the latter technique, part of an annular hollow portion is defined by welding a separate segment, or by molding an annular flange simultaneously when the rim is formed and then causing the flange to fall in a sloping fashion so as to define a hollow portion. Although it is a superior method that the annular flange is molded integrally with the rim so as to erect in a diametrical direction of a wheel when the rim is molded, a quite large number of preparation steps are necessary to cause the annular flange so integrally molded to fall in a curved fashion into a substantially L-shape. The increase in the number of steps constitutes a causes for an increase in production costs, and therefore, a further simple and easy method is desired. The invention was made in view of these situations.